Department of Freshwater and Marine Ecology (FAME), Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, P.O. Box 94920, 1090 XH, Amsterdam, The Netherlands.
Ecology of Marine Microbes, Institut de Ciènces del Mar (ICM-CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Catalonia, Spain.
Harmful Algae. 2022 Aug;117:102292. doi: 10.1016/j.hal.2022.102292. Epub 2022 Jul 28.
Phaeocystis is a globally widespread marine phytoplankton genus, best known for its colony-forming species that can form large blooms and odorous foam during bloom decline. In the North Sea, Phaeocystis globosa typically becomes abundant towards the end of the spring bloom, when nutrients are depleted and the share of mixotrophic protists increases. Although mixotrophy is widespread across the eukaryotic tree of life and is also found amongst haptophytes, a mixotrophic nutrition has not yet been demonstrated in Phaeocystis. Here, we sampled two consecutive Phaeocystis globosa spring blooms in the coastal North Sea. In both years, bacterial cells were observed inside 0.6 - 2% of P. globosa cells using double CARD-FISH hybridizations in combination with laser scanning confocal microscopy. Incubation experiments manipulating light and nutrient availability showed a trend towards higher occurrence of intracellular bacteria under P-deplete conditions. Based on counts of bacteria inside P. globosa cells in combination with theoretical values of prey digestion times, maximum ingestion rates of up to 0.08 bacteria cell h were estimated. In addition, a gene-based predictive model was applied to the transcriptome assemblies of seven Phaeocystis strains and 24 other haptophytes to assess their trophic mode. This model predicted a phago-mixotrophic feeding strategy in several (but not all) strains of P. globosa, P. antarctica and other haptophytes that were previously assumed to be autotrophic. The observation of bacterial cells inside P. globosa and the gene-based model predictions strongly suggest that the phago-mixotrophic feeding strategy is widespread among members of the Phaeocystis genus and other haptophytes, and might contribute to their remarkable success to form nuisance blooms under nutrient-limiting conditions.
聚球藻是一种广泛分布于全球的海洋浮游植物属，以其形成群体的物种而闻名，这些物种在衰退时会形成大量的水华和有气味的泡沫。在北海，聚球藻通常在春季水华结束时变得丰富，此时营养物质耗尽，混合营养型原生生物的比例增加。尽管混合营养在真核生物的生命之树上很普遍，也存在于甲藻中，但聚球藻中尚未证明存在混合营养。在这里，我们在北海沿海地区连续两个春季水华期间采样了聚球藻。在这两年中，使用双 CARD-FISH 杂交结合激光扫描共聚焦显微镜，在 0.6-2%的聚球藻细胞中观察到细菌细胞。操纵光照和营养供应的培养实验表明，在 P 缺乏条件下，细胞内细菌的出现率呈上升趋势。基于聚球藻细胞内细菌的计数以及猎物消化时间的理论值，估计最大的吞噬率高达 0.08 个细菌细胞 h。此外，应用基于基因的预测模型对 7 株聚球藻和 24 株其他甲藻的转录组组装进行了分析，以评估它们的营养模式。该模型预测了几种（但不是所有）聚球藻、南极聚球藻和其他甲藻的吞噬混合营养摄食策略，这些藻以前被认为是自养的。在聚球藻内观察到细菌细胞以及基于基因的模型预测强烈表明，吞噬混合营养摄食策略在聚球藻属和其他甲藻的成员中广泛存在，并且可能有助于它们在营养限制条件下形成大量水华的显著成功。
